It is known that mono- and diesters of alkylene glycols can be synthesized by reacting a carboxylic acid with an olefin and a nitrogen-oxygen containing compound; using a soluble palladium compound as a catalyst. During the reaction, the palladium compound gradually reacts with ingredients of the reaction system to form an insoluble palladium-containing precipitate which is catalytically inactive.
The precipitate is insoluble in organic solvents and in most mineral acids. It is soluble in aqua regia, but the use of this solvent is not commercially desirable. The precipitate is also soluble in strong aqueous alkaline media.
One method of recovering palladium from the precipitate is described in U.S. Pat. No. 3,655,363. The procedure consists of dissolving the precipitate in aqueous alkali metal hydroxide, alkali metal cyanide or ammonia. The palladium-containing mixture is then reduced to metallic palladium with hydrazine, hydrogen or formaldehyde. Then metallic palladium is recovered by filtration. A process which eliminates the isolation of the precipitate formed during the formation of the monoester and the filtration and recovery of the reduced palladium thereafter is desirable, since it would decrease the palladium loss and also decrease the number of steps in the reactivation procedure.